1. Field of the Invention
The present invention relates to a phenolic resin molding material with excellent low-pressure moldability. More particularly, the invention is intended to provide a phenolic resin molding material which scarcely allows formation of flash during injection molding.
2. Related Art Statement
Phenolic resin molding materials are utilized for a wide range of applications such as automobile parts, electronic and electrical parts, machine parts, etc., because of their high heat resistance and excellent electrical and mechanical properties. However, phenolic resin molding materials have the problem that they tend to form flash during molding as compared with thermoplastic resin molding materials. Flash is formed as the molten molding material is forced out from the narrow spaces such as parting face, air vent, etc., of a mold during molding. A great deal of time and labor is required for removing flash from the molded products, so that reduction or inhibition of flash formation in working of the phenolic resin molding materials has been strongly desired.
As a solution to this problem, it has been proposed to blend a powdery filler in the molding material. However,when it is tried to inhibit flash formation by this method, the fluidity of the molding material is deteriorated, causing incomplete filling of the mold cavity with the molding material. It was thus difficult for this method to satisfy both requirements for inhibition of flash formation and perfect filling of the mold cavity with the molding material. Many proposals regarding design of a mold and design and control of a molding machine have been made for the solution of the subject problem, but none of these proposals could give a practical solution to the problem. Low-pressure molding with a low-condensation novolak has also been proposed, but this method had the problem of low curing rate and could hardly be put to practical use.